The invention relates to interconnect networks for parallel processing systems. In a parallel processing system, a number of processing nodes are interconnected and operated as a single, coherent computing machine.
Generally, a switching network comprises a multitude of identical integrated circuit switch elements that are interconnected in a manner which provides a high bandwidth, low latency communication path between any pair of processing nodes. The size of networks of this type can be large. The number of switch elements needed to implement an omega network topology, for example, varies as (N/n) log.sub.n N where N denotes the number of processing nodes, and 2n is the number of ports associated with a single switch element. Thus, for a switch element having four duplex ports or eight simplex ports (n=4), the number of switch elements needed for a 16,384 node system is 28,672. To further emphasize the size and complexity of these networks, it may be noted that each switch element is generally connected to 2n other switch elements, resulting in a layout and wiring problem of large proportions. Understandably, therefore, such networks are difficult to design and develop, and the diagnosis of even routine hardware or software failures can be a difficult task.
The practical utilization of networks of this size and complexity thus requires that they be serviced entirely under computer control. Such servicing embraces a wide variety of tasks, such as measurement of transmission parameters, initialization of the network, monitoring of individual elements, diagnosis of failures, and error recovery. Existing approaches to meeting this service requirement involve various forms of completely separate service networks that operate effectively in parallel with what may be called the user network. The designations "service" and "user" are chosen to emphasize the distinctly different functions of the two networks. This approach creates a hybrid network that requires additional connectivity at each switch element, and additional wiring. This additional complexity increases the cost of the whole system. Yet, even with a hybrid network, it is still difficult to fully observe individual elements of the user network while the user network is in operation.